docs: document JS SDK installation (#9611)

- Add a page introducing JS SDK + how to install and use it (generally)
- Adjust admin tips on how to send requests
- Adjust storefront tips to mention JS SDK
- Add in the API reference intro how to install JS SDK
- Other related additions / changes

Closes DX-957

www/apps/api-reference/app/_mdx/client-libraries.mdx

@@ -8,11 +8,15 @@ Check out the [Medusa v2 Documentation](https://docs.medusajs.com/v2).
 
 <Space bottom={8} />
 
-<Note type="soon">
+<H3 className="!mt-0">Medusa JS SDK</H3>
 
-JavaScript client libraries are coming soon for Medusa v2.
+To use Medusa's JS SDK library, install the following packages in your project (not required for admin customizations):
 
-</Note>
+```bash
+npm install @medusajs/js-sdk@rc @medusajs/types@rc
+```
+
+Learn more about the JS SDK in [this documentation](https://docs.medusajs.com/v2/resources/js-sdk).
 
 ### Download Full Reference